Detection and modelling of electrode topography effects on particle traps

Abstract

Spatially resolved optical emission from an argon discharge is used to detect regions of enhanced emission over a grooved electrode designed to trap and channel particles. A groove extends the entire length of the electrode and is aligned with the optical detection axis. Thus we measure the integrated line-of-sight emission inside, above and next to the groove. Enhanced emission is seen and shown to be pressure-dependent for a given groove design. At low pressure (<100 mTorr) a single 'bright' spot is noted above the centre of the groove. This spot splits into two with increasing separation as the pressure increases. Laser light scattering detection of suspended particles shows correlated splitting of a single trapping region at low pressure into two traps at higher pressure. A two-dimensional radiofrequency discharge model is applied to the grooved electrode. The model consists of solving the electron, ion and continuity equations, the electron energy balance and Poisson's equation over the two-dimensional domain. The drift-diffusion approximation is used for electron and ion fluxes. Model results of the ionization rate are in reasonable agreement with experimental measurements. The resulting potential profiles from the model solution may be used to analyse particle trap locations.